On Thu, 16 Jan 2025 07:25:08 +0100,
John Stultz wrote:
>
> Betty reported hitting the following warning:
>
> [ 8.709131][ T221] WARNING: CPU: 2 PID: 221 at kernel/workqueue.c:4182
> ...
> [ 8.713282][ T221] Call trace:
> [ 8.713365][ T221] __flush_work+0x8d0/0x914
> [ 8.713468][ T221] __cancel_work_sync+0xac/0xfc
> [ 8.713570][ T221] cancel_work_sync+0x24/0x34
> [ 8.713667][ T221] virtsnd_remove+0xa8/0xf8 [virtio_snd
> ab15f34d0dd772f6d11327e08a81d46dc9c36276]
> [ 8.713868][ T221] virtsnd_probe+0x48c/0x664 [virtio_snd
> ab15f34d0dd772f6d11327e08a81d46dc9c36276]
> [ 8.714035][ T221] virtio_dev_probe+0x28c/0x390
> [ 8.714139][ T221] really_probe+0x1bc/0x4c8
> ...
>
> It seems we're hitting the error path in virtsnd_probe(), which
> triggers a virtsnd_remove() which iterates over the substreams
> calling cancel_work_sync() on the elapsed_period work_struct.
>
> Looking at the code, from earlier in:
> virtsnd_probe()->virtsnd_build_devs()->virtsnd_pcm_parse_cfg()
>
> We set snd->nsubstreams, allocate the snd->substreams, and if
> we then hit an error on the info allocation or something in
> virtsnd_ctl_query_info() fails, we will exit without having
> initialized the elapsed_period work_struct.
>
> When that error path unwinds we then call virtsnd_remove()
> which as long as the substreams array is allocated, will iterate
> through calling cancel_work_sync() on the uninitialized work
> struct hitting this warning.
>
> The simplest fix seems to just check the work_struct->func ptr
> is valid before calling cancel_work_sync(), but I wanted to share
> in case folks had ideas for a better solution.
>
> I have not yet managed to reproduce the issue myself, so this
> patch has had limited testing.
>
> Feedback or thoughts would be appreciated!
The conditional canceling is a bit flaky, IMHO.
Alternatively, we can initialize the whole stuff right after the
allocation, e.g. something like below.
thanks,
Takashi
--- a/sound/virtio/virtio_pcm.c
+++ b/sound/virtio/virtio_pcm.c
@@ -339,6 +339,16 @@ int virtsnd_pcm_parse_cfg(struct virtio_snd *snd)
if (!snd->substreams)
return -ENOMEM;
+ for (i = 0; i < snd->nsubstreams; ++i) {
+ struct virtio_pcm_substream *vss = &snd->substreams[i];
+
+ vss->snd = snd;
+ vss->sid = i;
+ INIT_WORK(&vss->elapsed_period, virtsnd_pcm_period_elapsed);
+ init_waitqueue_head(&vss->msg_empty);
+ spin_lock_init(&vss->lock);
+ }
+
info = kcalloc(snd->nsubstreams, sizeof(*info), GFP_KERNEL);
if (!info)
return -ENOMEM;
@@ -352,12 +362,6 @@ int virtsnd_pcm_parse_cfg(struct virtio_snd *snd)
struct virtio_pcm_substream *vss = &snd->substreams[i];
struct virtio_pcm *vpcm;
- vss->snd = snd;
- vss->sid = i;
- INIT_WORK(&vss->elapsed_period, virtsnd_pcm_period_elapsed);
- init_waitqueue_head(&vss->msg_empty);
- spin_lock_init(&vss->lock);
-
rc = virtsnd_pcm_build_hw(vss, &info[i]);
if (rc)
goto on_exit;
